Change congestion protocol in Solaris 10

I have a client with a meshed Cisco backbone.
6500's on top, Nexus 7000 in the middle and 4500's in bottom.

Solaris 10 servers connected to the 4500's backing up to a RedHat Linux backup server connected to the Nexus 7000's. The traffic is routed from 4500 --> Nexus 7000 --> 6500 --> Nexus 7000 --> backup server.

Backup clients have 1 GbE interfaces, backbone is 10GbE and backup server has 10 GbE interfaces.

Speed is good for all backup clients but not for the Solaris 10 backup clients. They have a short spike for anything between 30 secs - 2 minutes and then falls down to about 250 kbps per save stream.

I heard this could probably be solved by changing the congestion protocol on the Solaris hosts as they are misaligned with RedHat congestion protocol. But I can't find how to change or look at that with Solaris 10???

Found an article that describes this for Solaris 11, but not for Solaris 10.

Anyone that can help me on how to do this on Solaris 10 or point me in any direction on how to solve this problem?

You probably mean TCP/IP tuning?
That can be done with ndd command

ndd /dev/tcp \?
ndd /dev/ip \?

And on the NIC driver, e.g. ifconfig -a shows ce0 then try

ndd /dev/ce \?
ndd /dev/ce0 \?

Check the man page how to change values

man ndd

But the first thing to do is to look for a NIC driver update/patch!

I am familiar with ndd, but cannot find how to change or view current congestion protocol used. In Solaris 11 there's a tool called ipadm, that I can use - but it's not available in Solaris 10.

Solaris 10 does not show a protocol - just Solaris 11. Solaris 10 has a bunch of tunables related to network congestion:
Main link:
Book Information (Solaris Tunable Parameters Reference Manual)

TCP manual (chap 3 I think)
Book Information (Solaris Tunable Parameters Reference Manual)

IF you search for "cwnd" and "cong" using your browser you get some the tunables related to your issue. There is no algorithm to set like CUBIC -- that Linux 2.6 uses. Solaris 10 u08 predates a lot of that development.

An older discussion on the problem - note the links to Sun sites are broken due to oracle's decision to redo everything.

Solaris - Tuning Your TCP/IP Stack